I had a bit of spare time and played around with the idea of incorporating a grid rotation option into my amended version of your program. Here's the result, which seems to work ok, both in LB and the LBB compiler:

I changed the code in my post #3 to add box borders to your program's output for both the starting grid and the solution.

I also included an error trap to print "No solution" if none found (eg, for puzzles incorrectly entered).

phrontister

2012-04-14 03:16:36

Hi hammana,

Thanks for that Wiki link. I didn't try to follow what they said there because I'm not really into sudokus anymore, but out of curiosity I ran the four 'hardest sudokus' in your program, and it solved them all.

I didn't compare the coding of the two programs, but you might find it interesting.

I also ran purecardmagic's GUI that incorporates fqvarfort's solver. It requires typing the initial puzzle cells into a typical sudoku-style grid, and it works well, but I prefer single-string entry for actions such as copy/pasting puzzles from other software and repeat puzzle entry.

fqvarfort's solver requires hard coding each puzzle into the program, doesn't display the original puzzle and outputs the solution as a string...and so I changed the code like I did yours.

An innovative freeware program I have is SudokuSusser, which is a very strong solver and good tutor. It supports image entry, whereby you can simply copy/paste a puzzle graphic from a website or your computer and run it in SS. Unfortunately it seems to be no longer supported, and it may be difficult to find a download for it.

I tried to see if the compiled version runs faster, but the .exe file i obtain does not work.

What compiler did you use? The only one I found that is specifically for LB is GLBCC - program and docs at lbpp.sourceforge.net/ - but I can't get it to work on my computer (Windows XP).

hammana

2012-04-13 21:16:49

Hi phrontister

http://en.wikipedia.org/wiki/Sudoku_algorithms

The above site discusses the various algorithms to solve Sudoku. I learned that I am using the "Brute Force Algorithm" which is the least elegant one. The site gives the worst case grid to show the disadvantage of this algorithm. In fact it ooks me 9 hours to solve it, but the same grid rotated 90 degrees is solved in 18 minutes. I tried tho see if the compiled version runs faster, but the .exe file i obtain does not work.

bobbym

2012-04-12 17:41:58

Hi phrontister;

Okay, I was just wondering whether you would show the code if you had written it.

phrontister

2012-04-12 14:21:32

Hi Bobby,

Do you mean the generator? The solver is hammana's. Anyway, I haven't written either.

The generator is one written by Henk Westhuis. It's called IntoSudoku, and I own a registered version of the software. It's a solver too, plus being a good teaching aid and worksheet.

When sudokus were all the rage I learnt some of the complex patterns so I could solve the diabolicals, but they bored me after a while and I've now lost interest in them. Scanning, scanning, scanning and more scanning of candidates...

I haven't done a sudoku for ages.

bobbym

2012-04-12 11:38:35

Hi phrontister;

Is your solver handwritten?

phrontister

2012-04-12 11:17:21

Hi hammana,

I ran my sudoku generator overnight to give it a good amount of time to come up with a more difficult puzzle than the ones I've been testing your solver with, and this was the one it rated as the hardest it found:

It took the solver nearly 7 minutes. That is quite a different result from the other tests, none of which went over 20 seconds.

I tested it in your original version and my altered one, with similar results.

I have several freeware solvers, and all of them found the solution pretty much instantaneously. Same with two online solvers I tried it on.

Interesting...

bobbym

2012-04-12 05:57:55

Ask around someone will provide you with a lot of help.

anonimnystefy

2012-04-12 05:55:54

I will see if the my school has Mathematica or any other useful math package.

bobbym

2012-04-12 05:48:32

Last time I saw it at 49 bucks american. But the prices change and may be different elsewhere. Your professor should know more about it than I do. Most college kids get it for nothing at school and then sort of take it home with them.

anonimnystefy

2012-04-12 05:44:49

How much is it for students?

bobbym

2012-04-12 05:38:07

149 dollars back then. It is much cheaper now, especially for students.